lib/tevent/tevent_signal.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    common events code for signal events
   5
   6    Copyright (C) Andrew Tridgell        2007
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "replace.h"
  23 #include "system/filesys.h"
  24 #include "system/wait.h"
  25 #include "tevent.h"
  26 #include "tevent_internal.h"
  27 #include "tevent_util.h"
  28
  29 #define NUM_SIGNALS 64
  30
  31 /* maximum number of SA_SIGINFO signals to hold in the queue */
  32 #define SA_INFO_QUEUE_COUNT 100
  33
  34 struct sigcounter {
  35         uint32_t count;
  36         uint32_t seen;
  37 };
  38
  39 #define SIG_INCREMENT(s) (s).count++
  40 #define SIG_SEEN(s, n) (s).seen += (n)
  41 #define SIG_PENDING(s) ((s).seen != (s).count)
  42
  43 struct tevent_common_signal_list {
  44         struct tevent_common_signal_list *prev, *next;
  45         struct tevent_signal *se;
  46 };
  47
  48 /*
  49   the poor design of signals means that this table must be static global
  50 */
  51 static struct sig_state {
  52         struct tevent_common_signal_list *sig_handlers[NUM_SIGNALS+1];
  53         struct sigaction *oldact[NUM_SIGNALS+1];
  54         struct sigcounter signal_count[NUM_SIGNALS+1];
  55         struct sigcounter got_signal;
  56         int pipe_hack[2];
  57 #ifdef SA_SIGINFO
  58         /* with SA_SIGINFO we get quite a lot of info per signal */
  59         siginfo_t *sig_info[NUM_SIGNALS+1];
  60         struct sigcounter sig_blocked[NUM_SIGNALS+1];
  61 #endif
  62 } *sig_state;
  63
  64 /*
  65   return number of sigcounter events not processed yet
  66 */
  67 static uint32_t sig_count(struct sigcounter s)
  68 {
  69         if (s.count >= s.seen) {
  70                 return s.count - s.seen;
  71         }
  72         return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
  73 }
  74
  75 /*
  76   signal handler - redirects to registered signals
  77 */
  78 static void tevent_common_signal_handler(int signum)
  79 {
  80         char c = 0;
  81         ssize_t res;
  82         SIG_INCREMENT(sig_state->signal_count[signum]);
  83         SIG_INCREMENT(sig_state->got_signal);
  84         /* doesn't matter if this pipe overflows */
  85         res = write(sig_state->pipe_hack[1], &c, 1);
  86 }
  87
  88 #ifdef SA_SIGINFO
  89 /*
  90   signal handler with SA_SIGINFO - redirects to registered signals
  91 */
  92 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
  93                                               void *uctx)
  94 {
  95         uint32_t count = sig_count(sig_state->signal_count[signum]);
  96         sig_state->sig_info[signum][count] = *info;
  97
  98         tevent_common_signal_handler(signum);
  99
 100         /* handle SA_SIGINFO */
 101         if (count+1 == SA_INFO_QUEUE_COUNT) {
 102                 /* we've filled the info array - block this signal until
 103                    these ones are delivered */
 104                 sigset_t set;
 105                 sigemptyset(&set);
 106                 sigaddset(&set, signum);
 107                 sigprocmask(SIG_BLOCK, &set, NULL);
 108                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 109         }
 110 }
 111 #endif
 112
 113 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 114 {
 115         DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 116         return 0;
 117 }
 118
 119 /*
 120   destroy a signal event
 121 */
 122 static int tevent_signal_destructor(struct tevent_signal *se)
 123 {
 124         struct tevent_common_signal_list *sl;
 125         sl = talloc_get_type(se->additional_data,
 126                              struct tevent_common_signal_list);
 127
 128         if (se->event_ctx) {
 129                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 130         }
 131
 132         talloc_free(sl);
 133
 134         if (sig_state->sig_handlers[se->signum] == NULL) {
 135                 /* restore old handler, if any */
 136                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 137                 sig_state->oldact[se->signum] = NULL;
 138 #ifdef SA_SIGINFO
 139                 if (se->sa_flags & SA_SIGINFO) {
 140                         talloc_free(sig_state->sig_info[se->signum]);
 141                         sig_state->sig_info[se->signum] = NULL;
 142                 }
 143 #endif
 144         }
 145
 146         return 0;
 147 }
 148
 149 /*
 150   this is part of the pipe hack needed to avoid the signal race condition
 151 */
 152 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 153                                 uint16_t flags, void *private)
 154 {
 155         char c[16];
 156         ssize_t res;
 157         /* its non-blocking, doesn't matter if we read too much */
 158         res = read(sig_state->pipe_hack[0], c, sizeof(c));
 159 }
 160
 161 /*
 162   add a signal event
 163   return NULL on failure (memory allocation error)
 164 */
 165 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 166                                                TALLOC_CTX *mem_ctx,
 167                                                int signum,
 168                                                int sa_flags,
 169                                                tevent_signal_handler_t handler,
 170                                                void *private_data,
 171                                                const char *handler_name,
 172                                                const char *location)
 173 {
 174         struct tevent_signal *se;
 175         struct tevent_common_signal_list *sl;
 176
 177         if (signum >= NUM_SIGNALS) {
 178                 errno = EINVAL;
 179                 return NULL;
 180         }
 181
 182         /* the sig_state needs to be on a global context as it can last across
 183            multiple event contexts */
 184         if (sig_state == NULL) {
 185                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 186                 if (sig_state == NULL) {
 187                         return NULL;
 188                 }
 189         }
 190
 191         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 192         if (se == NULL) return NULL;
 193
 194         se->event_ctx           = ev;
 195         se->signum              = signum;
 196         se->sa_flags            = sa_flags;
 197         se->handler             = handler;
 198         se->private_data        = private_data;
 199         se->handler_name        = handler_name;
 200         se->location            = location;
 201         se->additional_data     = NULL;
 202
 203         sl = talloc(se, struct tevent_common_signal_list);
 204         if (!sl) {
 205                 talloc_free(se);
 206                 return NULL;
 207         }
 208         sl->se = se;
 209         se->additional_data     = sl;
 210
 211         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 212         if (!talloc_reference(se, sig_state)) {
 213                 talloc_free(se);
 214                 return NULL;
 215         }
 216
 217         /* only install a signal handler if not already installed */
 218         if (sig_state->sig_handlers[signum] == NULL) {
 219                 struct sigaction act;
 220                 ZERO_STRUCT(act);
 221                 act.sa_handler = tevent_common_signal_handler;
 222                 act.sa_flags = sa_flags;
 223 #ifdef SA_SIGINFO
 224                 if (sa_flags & SA_SIGINFO) {
 225                         act.sa_handler   = NULL;
 226                         act.sa_sigaction = tevent_common_signal_handler_info;
 227                         if (sig_state->sig_info[signum] == NULL) {
 228                                 sig_state->sig_info[signum] = talloc_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 229                                 if (sig_state->sig_info[signum] == NULL) {
 230                                         talloc_free(se);
 231                                         return NULL;
 232                                 }
 233                         }
 234                 }
 235 #endif
 236                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 237                 if (sig_state->oldact[signum] == NULL) {
 238                         talloc_free(se);
 239                         return NULL;
 240                 }
 241                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 242                         talloc_free(se);
 243                         return NULL;
 244                 }
 245         }
 246
 247         DLIST_ADD(se->event_ctx->signal_events, se);
 248         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 249
 250         talloc_set_destructor(se, tevent_signal_destructor);
 251         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 252
 253         /* we need to setup the pipe hack handler if not already
 254            setup */
 255         if (ev->pipe_fde == NULL) {
 256                 if (sig_state->pipe_hack[0] == 0 &&
 257                     sig_state->pipe_hack[1] == 0) {
 258                         if (pipe(sig_state->pipe_hack) == -1) {
 259                                 talloc_free(se);
 260                                 return NULL;
 261                         }
 262                         ev_set_blocking(sig_state->pipe_hack[0], false);
 263                         ev_set_blocking(sig_state->pipe_hack[1], false);
 264                 }
 265                 ev->pipe_fde = tevent_add_fd(ev, ev, sig_state->pipe_hack[0],
 266                                              TEVENT_FD_READ, signal_pipe_handler, NULL);
 267                 if (!ev->pipe_fde) {
 268                         talloc_free(se);
 269                         return NULL;
 270                 }
 271         }
 272
 273         return se;
 274 }
 275
 276
 277 /*
 278   check if a signal is pending
 279   return != 0 if a signal was pending
 280 */
 281 int tevent_common_check_signal(struct tevent_context *ev)
 282 {
 283         int i;
 284
 285         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 286                 return 0;
 287         }
 288
 289         for (i=0;i<NUM_SIGNALS+1;i++) {
 290                 struct tevent_common_signal_list *sl, *next;
 291                 struct sigcounter counter = sig_state->signal_count[i];
 292                 uint32_t count = sig_count(counter);
 293
 294                 if (count == 0) {
 295                         continue;
 296                 }
 297                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 298                         struct tevent_signal *se = sl->se;
 299                         next = sl->next;
 300 #ifdef SA_SIGINFO
 301                         if (se->sa_flags & SA_SIGINFO) {
 302                                 int j;
 303                                 for (j=0;j<count;j++) {
 304                                         /* note the use of the sig_info array as a
 305                                            ring buffer */
 306                                         int ofs = ((count-1) + j) % SA_INFO_QUEUE_COUNT;
 307                                         se->handler(ev, se, i, 1,
 308                                                     (void*)&sig_state->sig_info[i][ofs],
 309                                                     se->private_data);
 310                                 }
 311                                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 312                                         /* we'd filled the queue, unblock the
 313                                            signal now */
 314                                         sigset_t set;
 315                                         sigemptyset(&set);
 316                                         sigaddset(&set, i);
 317                                         SIG_SEEN(sig_state->sig_blocked[i],
 318                                                  sig_count(sig_state->sig_blocked[i]));
 319                                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 320                                 }
 321                                 if (se->sa_flags & SA_RESETHAND) {
 322                                         talloc_free(se);
 323                                 }
 324                                 continue;
 325                         }
 326 #endif
 327                         se->handler(ev, se, i, count, NULL, se->private_data);
 328                         if (se->sa_flags & SA_RESETHAND) {
 329                                 talloc_free(se);
 330                         }
 331                 }
 332                 SIG_SEEN(sig_state->signal_count[i], count);
 333                 SIG_SEEN(sig_state->got_signal, count);
 334         }
 335
 336         return 1;
 337 }